The invention relates to a process and an arrangement for the piecing of a double yarn after a yarn breakage at a spinning unit of a spinning machine having a plurality of spinning units which each contain devices for the prestrengthening of two yarns and devices for winding these yarns, as a double yarn, onto a spool package which is used as a feeding spool package for a subsequent twisting. A newly spun double yarn and an end of the double yarn withdrawn from the spool package are connected with one another by splicing for a piecing.
The double yarn, which consists of two only prestrengthened yarns, on the whole, has a relatively low strength, so that its handling is critical during a piecing operation and may easily result in a breaking of the newly spun double yarn or of the double yarn withdrawn from the spool package.
An object of the invention is to provide a process and an arrangement in which the danger of a tearing of the double yarns during a piecing attempt is reduced.
This object is achieved in that, before the splicing, the newly pieced double yarn as well as the double yarn withdrawn from the spool package are prestrengthened by being provided with a twist.
By means of this twist, the double yarns are at least partially strengthened so that their handling presents less of a risk.
In a further development of preferred embodiments of the invention, it is provided that the double yarn taken from the spool package and the newly spun double yarn, over at least approximately the same lengths, receive a twist which is, in each case, in the opposite direction with respect to one another. After the spliced connection is established, a yarn piece will then be obtained which is twisted in the opposite direction in front of and behind the spliced connection; i.e., it has a type of false twist. These twists may then cancel themselves out, so that Practically no twist is contained in the final product.
In another development of preferred embodiments of the invention, it is provided that the double yarn which is taken off the spool package, and the newly spun double yarn each receive a twist in the same direction which is opposite of the subsequent twisted-yarn twist. During the Piecing, i.e., when the spliced connection is established, both yarns therefore receive a twist in the same direction. This twist will be at least partially cancelled during the subsequent twisting operation.
In a further development of preferred embodiments of the invention, it is provided in an arrangement that the devices for the picking-up of the newly spun double yarn and the devices for taking the double yarn off the spool package each contain a suction gripper which is equipped with a pneumatic twisting device affecting the respective double yarn. By means of this construction, the pneumatic twisting devices can easily be integrated into the arrangement without the requirement of any additional space and mainly without the requirement of any additional work steps during the piecing.
In a further development of preferred embodiments of the invention, it is provided that the suction grippers are equipped with devices for producing a true twist in the respective ends of the double yarns. In this case, it will be expediently provided that the suction grippers are provided with devices for cutting the double yarn at a distance from their mouths. These devices each produce a free end of the double yarn, so that a true twist is produced in the part located in front of it.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.